/Engine/Source/Runtime/UMG/Public/Blueprint/GameViewportSubsystem.h
Update the slot info of a previously added widget or Store the slot info for later use.
void SetWidgetSlot ( [UWidget](API\Runtime\UMG\Components\UWidget) * Widget, [FGameViewportWidgetSlot](API\Runtime\UMG\Blueprint\FGameViewportWidgetSlot) Slot )